Reflective diffraction of radiation beams for image registration

ABSTRACT

In a method of registering an image on a substrate, the substrate is placed on a substrate support and a radiation beam is directed toward the substrate. The radiation beam is reflectively diffracted to modulate the intensity of the radiation beam. The modulated radiation beam is scanned across the substrate to register an image on the substrate. In one version, the radiation beam is a laser beam which is projected onto a mask blank to form a mask.

CROSS-REFERENCE

[0001] This application is a divisional application of U.S. patentapplication Ser. No. 09/976,978, filed on Oct. 11, 2001, which isincorporated herein by reference in its entirety.

BACKGROUND

[0002] Embodiments of the present invention relate to the registrationof an image on a substrate.

[0003] An image registration apparatus scans one or more radiation beamson a substrate to register an image on the substrate. The radiationbeams are modulated or patterned in accordance with the image to beregistered onto the substrate. A typical image registration apparatuscomprises a substrate support and radiation beam source, focusing,modulating, and scanning components, to generate and modulate aradiation beam to form an image on the substrate. The substrate may be,for example, a mask blank to be used in the fabrication ofsemiconductors, and which is exposed to the modulated radiation beam toregister an circuit image onto photosensitive material of the maskblank. The mask blank is then developed and stabilized to form a mask tobe used in the fabrication of integrated circuits.

[0004] It is desirable to increase the image registration speeds togenerate high resolution images with good throughput. However, imageregistration speeds are often limited by the speed of the radiation beammodulators that modulate the intensities of the radiation beams. Forexample, one commonly used radiation beam modulator is an acousto-opticmodulator (AOM) which modulates a radiation beam by constructive anddestructive interference of the radiation beam. A typical AOM is capableof modulating about 32 beams at a rate of about 50 MHz and within about16 grayscale levels to provide an image data processing speed of about1.6 GHz. While such image data processing speeds are acceptable forconventional image registration methods, faster data throughput is oftenrequired to register images having higher levels of complexity and finerline widths.

[0005] Thus, it is desirable to have an image registration apparatus andmethod that provides higher image registration speeds withoutsacrificing image resolution. It is also desirable to provide the higherdata throughput rates consistently and reliably.

SUMMARY

[0006] In a method of registering an image on a substrate, the substrateis placed on a substrate support and a radiation beam is directed towardthe substrate. The radiation beam is reflectively diffracted to modulatethe intensity of the radiation beam. The modulated radiation beam isscanned across the substrate to register an image on the substrate.

[0007] A method of registering an image on a mask blank comprisesplacing a mask blank on a substrate support; directing a laser beamtoward the mask blank; splitting the laser beam into a plurality oflaser beamlets; reflectively diffracting the radiation beamlets tomodulate the intensities of the laser beamlets by adjusting a pluralityof adjustable reflectors between first and second positions whilemaintaining a plurality of fixed reflectors at a fixed position; andscanning the modulated laser beamlets across the mask blank to registeran image on the mask blank.

[0008] A method of registering an image on a mask blank comprisesplacing a mask blank on a substrate support and moving the substratesupport; projecting a laser beam toward the mask blank; splitting thelaser beam into a plurality of laser beamlets; modulating the laserbeamlets by applying a signal at a modulation frequency of less thanabout 10 MHz to at least about 160 reflector clusters, each reflectorcluster comprising a plurality of fixed and adjustable reflectors thatreflectively diffract the laser beamlets, wherein the adjustablereflectors are adjustable between first and second positions and thefixed reflectors are maintained at fixed positions; and scanning themodulated radiation beam across the mask blank to register an image maybe registered on the mask blank.

DRAWINGS

[0009] These features, aspects, and advantages of the present inventionwill become better understood with regard to the following description,appended claims, and accompanying drawings which illustrate examples ofthe invention. However, it is to be understood that each of the featurescan be used in the invention in general, not merely in the context ofthe particular drawings, and the invention includes any combination ofthese features, where:

[0010]FIG. 1 is a schematic diagram of an image registration apparatusaccording to an embodiment of the present invention showing a beammodulating component comprising an adjustable reflective diffractiongrating;

[0011]FIG. 2 is a schematic top view of an adjustable reflectivediffraction grating showing clusters of reflectors that each modulate aradiation beamlet;

[0012]FIG. 3a is a schematic sectional front view of an exemplaryreflector cluster;

[0013]FIG. 4a is a schematic perspective view of the reflector clusterof FIG. 3a;

[0014]FIG. 3b is a schematic sectional side view of the reflectorcluster of FIG. 3a showing the adjustable reflectors in their firstpositions;

[0015]FIG. 3c shows the reflector cluster of FIG. 3b with the adjustablereflectors in their second positions;

[0016]FIG. 4b is a schematic side view of a reflector cluster havingfixed and adjustable reflectors, showing the adjustable reflectors intheir first position;

[0017]FIG. 4c shows the reflector cluster of FIG. 4b with the adjustablereflectors in their second positions to reflectively diffract anincident radiation beam; and

[0018]FIG. 5 is a schematic top view of an adjustable reflectivediffraction grating that receives a single radiation beam and diffractsthe beam into a number of radiation beamlets.

DESCRIPTION

[0019] A radiation beam image registration apparatus according to thepresent invention may be used to register an image on a substrate. Anexemplary version of an apparatus 100, as schematically illustrated inFIG. 1, is suitable for registering an image, which is typically apattern representative of electronic circuitry or an electronic device,on a substrate 104, for example, a substrate suitable for use in thefabrication of integrated circuits. For example, the apparatus 100 maybe a mask-making apparatus suitable for registering the image on asubstrate 104, such as a mask blank. The substrate 104 is exposed in theapparatus 100 to a modulated radiation beam to register an image inphotosensitive material of the mask blank. The mask blank is thendeveloped and stabilized to fix the image and used in the fabrication ofintegrated circuits. The illustrative version of the apparatus 100provided herein should not be used to limit the scope of the invention,and the invention encompasses equivalent or alternative versions, aswould be apparent to one of ordinary skill in the art.

[0020] Generally, the apparatus 100 comprises a substrate support 108capable of supporting the substrate 104. The substrate support 108 has asupport motor 112 to move the substrate support 108 to position thesubstrate 104. For example, the support motor 112 may comprise anelectric motor capable of translating the substrate support 108 in the xand y directions along an x-y plane parallel to the substrate surface,rotate the substrate support 108, move the substrate support 108vertically up and down along the axis orthogonal to its plane, or tiltthe substrate support 108. Support position sensors 116 are capable ofprecisely determining the position of the substrate support 108 and ofthe substrate 104 itself. For example, the support position sensors 116may operate by reflecting a light beam (not shown) from the substratesupport 108 and measuring the position interferometrically. A vacuumpump 120 and vacuum port 122, which may be a channel extendingcircumferentially below the substrate 104, are provided to securely holdthe substrate 104 by vacuum force.

[0021] A radiation beam source 124 is provided to generate a radiationbeam 128 that travels along a radiation beam path 132 to the substrate104. The radiation beam source 124 may be, for example, a substantiallycoherent light source, such as a laser beam source, or an incoherentlight source, producing light in the ultraviolet, visible, or infraredparts of the frequency spectrum. In the exemplary version, the radiationbeam source 124 generates a collimated multi-wavelength radiation beam,such as continuous-wave ultraviolet laser beam having primary spectrallines at wavelengths 351 nm, 364 nm and 380 nm, and emanating from anArgon ion laser, commercially available from Coherent, Inc., SantaClara, Calif. Multiple radiation beam sources may also be used insteadof a single radiation beam source.

[0022] A number of beam modulating components 136 are in the radiationbeam path 132 to modulate the radiation beam 128. The components 136 mayinclude an optical relay 140 to transport the radiation beam 128 alongthe beam path 132 from the radiation beam source 124 to an active beamstabilizer 144. The optical relay 140 comprises optical elements capableof passively shaping the radiation beam 128 to a suitable shape. Thecomponents 136 may also include an active beam stabilizer 144 havingoptical elements which are capable of adjusting and maintaining astabilized position of the radiation beam 128.

[0023] In one version, a beam splitter 148 splits the radiation beam 128into a plurality of radiation beamlets 152. The beam splitter 148 maycomprise a number of parallel plates that split the radiation beam 128into a number of spatially separated beamlets 152 that each haveapproximately the same beam intensity, as for example, described in U.S.Pat. No. 5,386,221, which is incorporated herein by reference in itsentirety. In another version, the beam splitter 148 is a diffractivebeam splitter comprising fixed diffraction gratings that are constructedto split the radiation beam 128 into a plurality of beamlets 152 havingdifferent orders, as for example, described in Feldman, et al., OpticsLetters, Vol. 14, pp. 479 to 481, which is incorporated herein byreference in its entirety. Suitable diffractive optical beam splitters148 are manufactured by Rochester Photonics Corp., Rochester, N.Y. Thebeam splitter 148 typically splits the radiation beam 128 into, forexample, from about 20 beamlets to about 2000 beamlets, and in oneversion about 32 beamlets. Thus, the radiation beam 128 may be a singlebeam, a number of beamlets, or a number of separate beams.

[0024] The beam modulating components 136 also include a beam intensitymodulator 156 capable of modulating the intensity of the radiation beam128. In one version, the beam intensity modulator 156 is an adjustablereflective diffraction grating 160 that diffracts the radiation beam128, as shown in FIG. 2. The adjustable reflective diffraction grating160 is capable of adjustably reflectively diffracting the radiation beam128. By reflectively diffracting it is meant that the adjustable grating160 operates by reflecting the radiation beam 128 in either a diffractedor a non-diffracted state. In one version, the adjustable grating 160comprises one or more reflectors 164 capable of reflectively diffractingthe radiation beam 128, in accordance with an applied electrical signalrelating to the image to be registered onto the substrate 104. Forexample, the reflectors 164 may be capable of diffracting the radiationbeamlets 152 to turn the beamlets 152 on and off and to control anintensity of the radiation beam 28 that is reflectively diffracted.

[0025] In one version, the reflectors 164 are arranged as one or moreclusters 168 that correspond to the configuration of the radiationbeamlets 152 so that each reflector cluster 168 modulates the intensityof a radiation beamlet 152, as for example, illustrated in FIG. 2. Anarray 169 of such reflector clusters 168 is capable of modulating aplurality of radiation beamlets 152. The array 169 may be formed byaligning the reflector clusters 168 substantially along a line in orderto modulate the intensity of a linearly spaced apart array of beamlets152 to form a “brush” that is capable of registering an image on thesubstrate 104. The array 169 may also comprise reflector clusters 168that are arranged according to a two-dimensional grid of reflectors 164comprising parallel lines of the arrays 169, for example, to correspondto a matching grid pattern of the radiation beamlets 152.

[0026] The adjustable reflective diffraction grating 160 comprises aplurality of fixed and adjustable reflectors 172, 176, respectively, tomodulate the radiation beamlets 152, as shown in FIGS. 3b and 3 c. Thefixed reflectors 172 remain in fixed positions relative to theadjustable reflectors 176. The adjustable reflectors 176 may bedisplaced relative to the fixed reflectors 172 to diffract the radiationbeamlets 152 and thereby modulate their intensities. For example, theadjustable reflectors 176 may be adjustable between first and secondpositions 175 a, 175 b, to controllably reflectively diffract theradiation beamlets 152. In one version, the first positions 175 a arenon-diffracting positions in which the radiation beamlets 152 are notdiffracted, as shown in FIG. 3b, and the second positions 175 b arediffracting positions in which the radiation beamlets 152 arediffracted, as shown in FIG. 3c. Generally, the reflectors 164 areshaped, sized, and arranged to cover a beam spot area of the radiationbeamlets 152 to diffract the radiation beamlets 152 across its entirebeam spot size. The shapes and sizes of the reflectors 164 and thespacing between the reflectors 164 affects the amount of radiationdiffracted. The shapes and sizes of the reflectors 164 may also beselected to control the image modulating speed. For example, smallerreflectors 176, 172 that diffract smaller beamlets 152 may provide ahigher modulation frequency and faster modulating times than largerreflectors 176, 172 that are capable of diffracting larger beamlets 152.

[0027] In one version, the fixed and adjustable reflectors 172, 176 areinterleaved with one another to define a substantially continuousreflecting surface, as shown in FIG. 4a. In this version, the fixed andadjustable reflectors 172, 176 are both shaped as elongated strands, forexample, having a ratio of length to width of at least about 10:1;however, other shapes may also be used. Each fixed reflector 172 issupported continuously along its length by a supporting material 186underneath the fixed reflector 172, while each adjustable reflector 176is displaceable at its middle portion. The reflectors 164 areinterleaved with one another and spaced apart at about the samedistances. The reflectors 164 comprise a material that is capable ofreflectively diffracting the radiation beamlets 152. In one version, thereflectors 164 comprise a core material 188 and a coating material 192.A suitable core material 188 is one that may be displaced or deformed,such as for example, silicon nitride. The coating material 192 reflectsthe radiation beamlets 152, and may be, for example, aluminum. Thereflectors 164 have downwardly bent tabs 196 which are anchored to awafer 200. The wafer 200 may comprise multiple layers including a toplayer 204, a middle layer 208, and a bottom layer 212, which aresuitable to support the reflectors 164. In one example, the top layer204 comprises tungsten, the middle layer 208 comprises oxide, and thebottom layer 212 comprises silicon. A plate 216 capable of beingmaintained at a voltage in relation to the adjustable reflectors 176 isembedded inside the wafer 200. The plate 216 comprises a materialsuitable to be set at a voltage in relation to the reflectors 164, suchas a conductor material, for example aluminum or silver, or a materialcapable of being electrostatically charged, for example aluminum orsilver. An exemplary adjustable reflective diffraction grating 160 ismanufactured by Silicon Light Machines, Inc., Sunnyvale, Calif.

[0028] Referring to FIGS. 4b and 4 c, the adjustable reflectivediffraction grating 160 of FIG. 4a is operated by providing a voltage tothe plate 216 underlying the reflectors 164. When no voltage is appliedto the plate 216 in relation to the adjustable reflectors 176, theadjustable reflectors 176 are in their first positions and flat andcoplanar to the fixed reflectors 172, as shown in FIGS. 3b and 4 b. Aradiation beamlet 152 a of the radiation beam that is incident on thereflectors 164 is specularly reflected at an angle of reflectionsubstantially equal to the angle of incidence, as a zero-order radiationbeamlet 220 which is blocked by a beam stop 228. However, when a voltageis applied to the plate 216 in relation to the adjustable reflectors176, the adjustable reflectors 176 are displaced from their firstunbiased positions 175 a to their second biased positions 175 b becausethey are attracted toward the voltage biased plate 216, as shown inFIGS. 3c and 4 c. When a radiation beamlet 152 a is incident on thereflectors 164, the radiation beamlet 152 a is diffracted, creatingbeamlets 152 other than the zero-order beamlet 220, such as afirst-order beamlet 224, which is diffracted back into the beam path132. Thus, the radiation beamlet 152 a does not pass through the beamintensity modulator 156 when no voltage is applied to the plate 216, andthe radiation beamlet 152 a does pass through the beam intensitymodulator 156 when a voltage is applied to the plate 216. In this way,the reflectors 164 serve as an on/off switch. Also, the reflectors 164may be used to fractionally tune the intensity of the reflectivelydiffracted first-order beamlet 224 by varying the voltage applied to theplate 216 because the intensity of the first-order beamlet 224corresponds to the applied voltage. For example, the intensity of thefirst-order beamlet 224 may correspond linearly to the applied voltage.While this example is illustrated for first-order diffracted beamlets224, higher-order beamlets, such as a second-order beamlet orthird-order beamlet, may also be passed in the “on” state; oralternatively, a zero-order beamlet 220 may be passed in the “on” state,and a higher-order beamlet blocked in the “off” state.

[0029] The adjustable reflectors 176 may be displaced by a distance thatis selected in relation to the wavelength of the radation beamlet 152.This version may be used to set a predetermined diffraction order of thediffracted radiation beamlet 152. For example, the displacement distancemay be about one quarter of the wavelength of the radiation beamlet 152a. In one version, the adjustable reflective diffraction grating 160 maybe used to modulate the intensities of the radiation beamlets 152 toreliably provide fractional beam intensities which are useful in theregistration of grayscale images. The amount of displacement of theadjustable reflectors 176 may be tailored by controlling the appliedvoltage to generate diffracted radiation beamlets 152 havingcontinuously variable intensities, for example, to replicate a grayscaleimage. The amount of displacement of the displaceable reflectors 176affects the intensity of each reflectively diffracted beamlet 152,thereby allowing fractional beam intensity modulation. Also, thecorrespondence between the applied voltage and the intensity of adiffracted beamlet 152, may be non-linear, which may make a lookup tableor functional approximation desirable to determine their relationship.

[0030] The voltage required to downwardly displace an adjustablereflector 176 from the first position is greater than the voltagerequired to upwardly displace an adjustable reflector 176 from thesecond position. In this case, a voltage of magnitude in between the twomay be used to maintain the reflectors 164 in an “on” state with almostno power consumption. This hysteresis effect may also be advantageouslyused with the run length encoded (RLE) compression scheme used by acontroller 228 of the apparatus 100. For example, a data stringcompressed in RLE might comprise a beam intensity command and a commandto copy 20 times. The beam intensity command can be delivered to thereflectors 164 as a displacement voltage, whereas the copy command canbe delivered to the reflectors 164 as a “maintain” voltage.

[0031] The radiation beam 128 may be also projected onto the adjustablereflective diffraction grating 160 to illuminate the entire grating 160,as shown in FIG. 5. This version may use the adjustable reflectivediffraction grating 160 to split the radiation beam 128 into theradiation beamlets 152, so that a dedicated beam splitter 148 is notneeded. In one version, the radiation beam 128 is cylindrically focusedto be of substantially uniform illumination intensity across the surfaceof the adjustable reflective diffraction grating 160. The signalsapplied to the individual reflector clusters 168 may also beindividually tuned or calibrated to compensate for significantlynonuniform illumination intensity, so that the diffracted beamletintensity level remains substantially constant. For example, thevoltages applied to the plates 216 of the individual reflector clusters168 may be adjustable.

[0032] The data throughput of the adjustable reflective diffractiongrating 160 is about proportional to the number of reflector clusters168 multiplied by the modulation rate of an individual reflector cluster168. An adjustable reflective diffraction grating 160 according to thepresent invention provides good image data processing rates whilemaintaining image resolution quality. For example, a typical adjustablereflective diffraction grating 160 is capable of modulating about 1,088beamlets within about 16 gray levels at a rate of about 50 MHz, whichcorresponds to about 54.4 GHz of data throughput. This is about 34 timesfaster than the exemplary data throughput rate achieved by aconventional imaging apparatus of about 1.6 GHz. In another embodiment,an adjustable reflective diffraction grating 160 having about 1088reflector clusters 168 that are modulated at about 1.6 MHz has about thesame data throughput as an adjustable reflective diffraction grating 160having about 32 reflector clusters 168 that are modulated at about 50MHz, or an acousto-optic modulator (not shown) having about 32 channelsthat are modulated at about 50 MHz.

[0033] In one version, only some of the reflectors 164 of the adjustablereflective diffraction grating 160 are used to modulate the radiationbeamlets 152, so that the image processing data throughput rate of thediffraction grating 160 matches the data throughput rate of the othercomponents. This version is useful when other components or parametersof the apparatus 100 provide lower data throughput capability than theadjustable reflective diffraction grating 160. In one example, since thespeed of the substrate support 108 that may be used is approximatelyproportional to the number of individual radiation beamlets 152, if thespeed of the substrate support 108 using all the reflectors 164 is toofast, the number of addressed reflectors 164 can be reduced until adesirable set speed of the substrate support 108 is achieved.

[0034] Returning to FIG. 1, after the radiation beamlets 152 aremodulated by the adjustable reflective diffraction grating 160, themodulated beamlets 152 are scanned across the substrate 108 to registerthe image on the substrate 104. The scanning may be performed by a beamscanner 236, such as for example, a rotating polygon mirror, that rasterscans the modulated radiation beamlets 152 along a scan direction acrossthe substrate 104, while the support motor 112 moves the substratesupport 108 in a direction substantially perpendicular to the scandirection. The polygon mirror rotates to change the angles of incidenceand reflection of the radiation beamlets 152 to scan the beamlets 152along a scanning stripe. A scan lens 240 translates the changing anglesof the beamlets 152 to a change in position of the beamlets 152. Areduction lens 244 reduces the size of the beam spot by a predefineddemagnification factor. The “scan rate” is the distance per unit timethat the beamlets 152 travel across the substrate 104 due to the motionof the support 108 as well as the motion of the beam scanner 236. Thescan rate is approximately equal to the product of the scan rate due tothe beam scanner 236 scanning the beamlets 152 across the substrate 104by displacing the beamlets 152 and the scan rate due to the supportmotor 112 scanning the beamlets 152 across the substrate 104 by movingthe substrate support 108 relative to the beamlets 152. The scan ratedesirable for an apparatus 100 is about equal to the pixel size of theimage multiplied by the modulation rate of the beam intensity modulator156. For example, for an image having a pixel size of about 100nanometers, beamlets 152 that are modulated by a beam intensitymodulator 156 having a modulation rate of about 50 MHz are scannedacross the substrate 104 at a total scan rate of about 5 m/s. For thesame pixel size, beamlets 152 being modulated by a beam intensitymodulator 156 having a modulation rate of about 1.6 MHz are scannedacross the substrate 104 at a total scan rate of about 160 mm/s.

[0035] The number of reflector clusters 168 and the modulation rate of amodulation signal applied to the beam intensity modulator 156 areselected to scan the radiation beam 128 across the substrate 104. Inanother version, the number of reflector clusters 168 and the modulationrate of the signal applied to the individual reflector clusters 168, areselected to allow the motion of the substrate support 108 to scan theradiation beamlets 152 across the substrate 104 without the use of aseparate beam scanner 236. This version of the apparatus 100 does notneed a separate beam scanner 236 because the scan rate is maintained atless than about 1 m/s at which speed the support motor 112 is capable ofmoving the substrate support 108. For example, the number of reflectorclusters 168 may be sufficiently increased, and the modulation rate ofthe signal applied to the individual reflector clusters 168 may besufficiently reduced, so that the motion of the substrate support 108generated by the support motors 112 is sufficiently fast to scan themodulated radiation beamlets 152 across the substrate 104. The reflectorclusters 168 are substantially aligned along a line to modulate alinearly spaced-apart array of beamlets 152 that forms a “brush” acrossthe substrate 104. The support motor 112 moves the substrate support 108to scan the beamlets 152 substantially across a first horizontal axis ofthe substrate 104. The support motor 112 then moves the substratesupport 108 (and substrate 104) upward along a vertical axissubstantially orthogonal to the first horizontal axis, and then movesthe substrate support 108 to scan the beamlets 152 substantially acrossa second horizontal axis of the substrate 104, which is below the firstaxis. This action is repeated to scan the beamlets 152 across the entiresurface of the substrate 104. In one version, a suitable number ofreflector clusters 168 is at least about 160 and maybe even at leastabout 300 clusters. Each cluster 168 modulates a single beamlet 152,thus, the number of the beamlets 152 needed is the same as the number ofclusters 168. In addition, the modulation rate of the signal applied tothe clusters 168 may also be reduced to less than about 10 Mhz or evenless than about 8 Mhz. An apparatus having 160 clusters 158 whosesignals are modulated at a rate of about 10 MHz, provide a scan rate ofless than about 1 m/s for a pixel size of about 100 nanometers whilemaintaining a typical data throughput for a conventional apparatus ofabout 1.6 GHz. In this version, the support motor 112 provides theentire scanning mechanism.

[0036] The number of clusters 158, and the number of radiation beamlets152 that can be modulated, may be limited by characteristics of theimage registration apparatus 100 to less than about 2000. For example,the size of the scan lens 240 may limit the number of radiation beamlets152 that can pass therethrough without substantial aberration. However,larger scan lenses 240 would allow the use of a larger number ofradiation beamlets 152.

[0037] In operation, the substrate 104, on which an image is to beregistered, is placed on, and held by, the substrate support 108. Afiducial mark locator 248 is provided to measure the actual locations offiducial marks 252 of the substrate 104 to determine the position of thesubstrate 104, substrate distortions, or mis-registrations. The fiducialmarks 252 may be holes, light reflective markings, diffraction gratings,or previously registered spots or images. The fiducial mark locator 248generally comprises an optical detector capable of detecting thefiducial marks 252 of the substrate 104, such as a charge-coupled device(CCD) camera. The optical detector monitors a change in the lighttransmitted through, or reflected back from, the substrate 104 todetermine the actual locations of the fiducial marks 252 of thesubstrate 104.

[0038] A controller 228 comprising a suitable configuration of hardware,software, or programmable logic devices, is adapted to control thesubstrate support 108, radiation beam source 124, and beam intensitymodulator 156 to modulate and scan the radiation beam 128 across thesubstrate 104 to register the image on the substrate 104. The controller228 is adapted to receive data, calculate the location of the substrate104 and any substrate distortion levels, determine a correction operatorfor the stored image, and operate the beam source 124 and beammodulating components 136. In one exemplary embodiment, the controller228 receives data of the measured locations of the fiducial marks 252and compares them to their original or design locations to determine thedeviation of each fiducial mark 252. The fiducial mark deviations areused to correct the encoded image to be registered on the substrate 104.The controller 228 then controls, for example, the adjustable reflectivediffraction grating 160, beam scanner 236, and scan lens 240 to registerthe correctly encoded image on the substrate 104. For example, thecontroller 228 sends signals to the beam intensity modulator 156 tocontrol pulsing of the radiation beamlets 152 to the desired intensitylevels and in correspondence to the image. The beam intensity modulator156 may also be controlled to scale the image in the scanning directionby timing the beamlet pulses. The support motor 112 also receives realtime instructions from the controller 228 to control the motion of thesubstrate support 108, and consequently the substrate 104, to scale,rotate, or translate the image projected on the substrate 104.Typically, an array of radiation beamlets 152 is scanned across thesubstrate 104 in nearly horizontal passes which are repeated along afirst vertical stripe, after which the beamlets 152 are scanned insecond horizontal passes along a second vertical stripe, and so forth.Thus, the controller 228 operates the radiation beam source 124,modulating components 176, and the support motor 112 to raster scan theradiation beamlets 152 across the substrate 104 in multiple passes.

[0039] The controller 228 may be a computer that executes software of acomputer-readable program residing in a computer system comprising acentral processing unit (CPU) 256, such as for example, a PentiumController commercially available from Intel Corporation, Santa Clara,Calif., that is coupled to a memory and peripheral computer components.The memory may comprise a computer readable medium having the computerreadable program therein. The memory may be hard disks 260, an opticalcompact disc (CD), floppy disk, random access memory (RAM) 264, or othertypes of volatile or non-volatile memory, suitable for storing fiducialmark locations, calculated fiducial mark deviations, correctionoperators, or corrected images.

[0040] The interface between a human operator and the controller 228 canbe, for example, via a display 268 and data input device 272, such as akeyboard. Other computer-readable programs such as those stored in othermemory including, for example, a floppy disk or other computer programproduct inserted in a drive of the memory may also be used to operatethe controller 228. The computer system card rack contains a singleboard computer, analog and digital input/output boards, interfaceboards, and stepper motor controller boards. Various components of theapparatus conform to the Versa Modular European (VME) standard, whichdefines board, card cage, and connector dimensions and types. The VMEstandard also defines the bus structure having a 16-bit data bus and24-bit address bus.

[0041] The computer-readable program generally comprises softwarecomprising a set of instructions to operate the radiation beam imageregistration apparatus 100. The computer-readable program can be writtenin any conventional programming language, such as for example, assemblylanguage, C, C++ or Pascal. Suitable program code is entered into asingle file, or multiple files, using a conventional text editor andstored or embodied in the memory of the computer system. If the enteredcode text is in a high-level language, the code is compiled, and theresultant compiler code is then linked with an object code ofpre-compiled library routines. To execute the linked, compiled objectcode, the user invokes the object code, causing the CPU 256 to read andexecute the code to perform the tasks identified in the program.

[0042] Thus, the present apparatus 100 and method is advantageousbecause it allows for improved throughput in modulating the intensitiesof radiation beams. Although the present invention has been described inconsiderable detail with regard to certain preferred versions thereof,other versions are possible. For example, the present invention could beused with other image registration apparatuses, such as an apparatusthat registers an image using substantially incoherent light. Thus, theappended claims should not be limited to the description of thepreferred versions contained herein.

What is claimed is:
 1. A method of registering an image on a substrate, the method comprising: (a) placing a substrate on a substrate support; (b) directing a radiation beam toward the substrate; (c) reflectively diffracting the radiation beam to modulate the intensity of the radiation beam; and (d) scanning the modulated radiation beam across the substrate to register an image on the substrate.
 2. A method according to claim 1 wherein (c) comprises adjusting a plurality of adjustable reflectors between first and second positions.
 3. A method according to claim 2 comprising adjusting the reflectors between a first diffracting position and a second non-diffracting position.
 4. A method according to claim 2 comprising maintaining a plurality of fixed reflectors at a fixed position while adjusting the adjustable reflectors.
 5. A method according to claim 2 comprising providing one or more reflector clusters of adjustable and fixed reflectors, and adjusting the adjustable reflectors in each cluster to reflectively diffract a radiation beamlet of the radiation beam.
 6. A method according to claim 5 comprising selecting the number of reflector clusters and the modulation rate of a modulation signal applied to the beam intensity modulator to scan the radiation beam across the substrate substantially absent a beam scanner.
 7. A method according to claim 6 comprising adjusting the adjustable reflectors in at least about 160 reflector clusters.
 8. A method according to claim 6 comprising selecting a modulation rate of less than about 10 MHz.
 9. A method according to claim 1 comprising scanning the radiation beam across the substrate by rotating a polygon mirror.
 10. A method of registering an image on a mask blank, the method comprising: (a) placing a mask blank on a substrate support; (b) directing a laser beam toward the mask blank; (c) splitting the laser beam into a plurality of laser beamlets; (d) reflectively diffracting the radiation beamlets to modulate the intensities of the laser beamlets by adjusting a plurality of adjustable reflectors between first and second positions while maintaining a plurality of fixed reflectors at a fixed position; and (e) scanning the modulated laser beamlets across the mask blank to register an image on the mask blank.
 11. A method according to claim 10 comprising providing one or more reflector clusters of adjustable and fixed reflectors, and adjusting the adjustable reflectors in each cluster to reflectively diffract a laser beamlet.
 12. A method according to claim 11 comprising selecting the number of reflector clusters and the modulation rate of a modulation signal applied to the beam intensity modulator to scan the laser beamlets across the mask blank substantially absent a beam scanner.
 13. A method according to claim 12 comprising adjusting the adjustable reflectors in at least about 160 reflector clusters.
 14. A method according to claim 13 comprising selecting a modulation rate of less than about 10 MHz.
 15. A method of registering an image on a mask blank, the method comprising: (a) placing a mask blank on a substrate support and moving the substrate support; (b) projecting a laser beam toward the mask blank; (c) splitting the laser beam into a plurality of laser beamlets; (d) modulating the laser beamlets by applying a signal at a modulation frequency of less than about 10 MHz to at least about 160 reflector clusters, each reflector cluster comprising a plurality of fixed and adjustable reflectors that reflectively diffract the laser beamlets, wherein the adjustable reflectors are adjustable between first and second positions and the fixed reflectors are maintained at fixed positions; and (e) scanning the modulated radiation beam across the mask blank to register an image may be registered on the mask blank.
 16. A method according to claim 15 wherein the reflector clusters are arranged substantially along a line.
 17. A method according to claim 15 wherein there are less than about 2000 reflector clusters. 